Chairs of the type provided with swiveling seats and supporting bases with integral central hubs of plastic construction are well-known in the art. Such swivel-type chairs generally include a central column preferably in the form of a gas, pneumatic or hydraulic cylinder between a seat of the chair and the base, permitting the seat to rotate and slide up or down along the longitudinal axis of the column as desired. In the past, chair bases have been formed of a welded metal subassembly including a central hub and a series of arms extending outwardly from the hub. The central column is mounted to the hub and casters are secured to each arm adjacent its outer end. A molded plastic shroud is engaged over the hub and arms to conceal the welded subassembly and enhance the aesthetic appearance of the base. Alternatively, the hub and arms may be formed of molded plastic, and a metallic insert positioned in a central throughbore of the hub. In either construction, a generally satisfactory seat was created so as to prevent wobbling or lateral deflection of the column relative to the base. However, because of problems in methods of manufacturing and holding manufacturing tolerances, there may not always be a snug fit between the metal column and the metal hub or insert, such that wobbling of these components will eventually occur, thereby resulting in undesirable and unacceptable rocking of the chair. Further, the need for the metal insert or welded metal subassembly adds to the overall cost of components and assembly of the base.
U.S. Pat. No. 5,377,943 issued to Perl on Jan. 3, 1995 shows a one-piece molded chair base in which the taper on the hub is removed and replaced with an internal step extending generally perpendicularly to upper and lower portions of the hub for engaging the bottom end of the column when the column is inserted into the throughbore of the hub. A further plastic molded base design is disclosed in U.S. Pat. No. 5,692,715 issued to Hertel on Dec. 2, 1997 which sets forth a dual tapered locking hub. A first tapered portion having a first taper angle is provided for a major portion in the length of the hub, and a second tapered portion having a second taper angle is provided in the remainder of the hub. The first taper angle on the hub cooperates with a similar tapered surface on the column to prevent wobbling of the column and the base. The second taper angle of the hub is greater than the first taper angle so as to lock the column in the hub and prevent creeping.
Notwithstanding the prior art, it remains desirable to provide a plastic molded base having an integral hub construction which not only prevents wobbling and creeping of the column relative to the base, but enables an economical and easily performed molding of the hub in the base. The present invention allows these advantages by providing positive seating between a column and a hub specially formed with differently tapered portions above and below a ring portion.
It is one object of the present invention to provide a chair base in which a gas cylinder is suitably mounted in a hub integral with the base and is supported so as to transfer its load onto the hub with the hub stabilizing the gas cylinder from wobbling relative to the base. It is also an object of the present invention to provide a molded chair base having an integral hub which allows ease of molding yet provides a combination of tapered and ring-shaped bearing surfaces to hold a gas cylinder steady in a throughbore of the hub. It is a further object of the present invention to provide a chair base hub having a throughbore defining an interior wall formed with an upper tapered portion for stabilizing a gas cylinder against lateral deflection and a ring portion for preventing the gas cylinder from moving downwardly relative to the base.
The invention contemplates a base for a swivel-type chair wherein the base includes a set of arms and a central hub for mounting and maintaining therein a central column joining the base with a seat of the chair. The hub is formed with a passage extending along a longitudinal axis coincident with a longitudinal axis of the central column. The passage defines a first wall portion tapered downwardly and inwardly relative to the longitudinal axis of the passage, and a second wall portion tapered downwardly and outwardly relative to the longitudinal axis of the passage. The central column is received within the passage and engages the first wall portion, and is thereby prevented from moving laterally and downwardly relative to the base. The hub further includes a ring portion projecting inwardly relative to the longitudinal axis of the passage and interconnecting the first wall portion and the second wall portion. The ring portion has an upper segment sloping downwardly and inwardly from the first wall portion, a medial segment extending vertically from the upper segment, and a lower segment sloping downwardly and outwardly from the medial segment. The central column includes an annular offset portion against which the upper segment of the ring portion is press fitted. The ring portion of the hub and the annular offset portion of the central column are located adjacent a bottom end of the arms. The first wall portion is located above the second wall portion, with the cross sectional area of the second wall portion being larger than the cross sectional area of the first wall portion. The second wall portion and the lower segment of the ring portion are spaced from the central column. The first wall portion has a length which is longer than the length of the second wall portion, while the second wall portion has a length which is longer than the length of the ring portion.
The invention further contemplates a chair base for a swivel-type chair wherein the base includes a central hub including a passage for receiving and engaging therein a central column of generally circular cross section joining the base with a seat of the chair. The invention contemplates the hub being provided with a primary bearing surface in the form of a major tapered wall portion sloping downwardly and inwardly at a first taper angle relative to the longitudinal axis of the passage, and a ring portion having at least a secondary bearing surface sloping downwardly and inwardly from the major tapered wall portion at a second taper angle greater than the first taper angle. With this construction, the major tapered wall portion prevents the central column from wobbling, and the secondary bearing surface prevents the central column from creeping through the base. The ring portion includes a tertiary bearing surface extending substantially vertically downwardly from the secondary bearing surface for further stabilizing the central column against wobbling, and a non-bearing surface extending downwardly and outwardly from the tertiary bearing surface. The passage includes a minor tapered wall portion sloping downwardly and outwardly from the non-bearing surface on the ring portion. The central column includes an upper portion shaped similarly to the major tapered wall portion of the hub, an angularly offset portion shaped similarly to the secondary bearing surface on the ring portion, and a lower, generally cylindrical portion formed with a diameter less than the diameter of the upper portion of the central column and spaced from the non-bearing surface and the minor tapered wall portion.
The invention also relates to a hub for the base of a swivel-type chair in which the hub includes a throughbore forming an interior wall which receives and retains therein a gas cylinder joining the throughbore with a seat of a chair. The interior wall of the hub is formed with an upper portion, a ring portion, and a lower portion. The upper portion slopes downwardly and inwardly at a first taper angle relative to a longitudinal axis of the gas cylinder and the throughbore. The ring portion has an upper segment sloping downwardly and inwardly from the upper portion at a second taper angle greater than the first taper angle, a medial segment extending vertically from the upper segment, and a lower segment sloping downwardly and outwardly from the medial segment at a third taper angle less than the second taper angle but greater than the first taper angle. The lower portion slopes downwardly and outwardly from the lower segment of the ring portion at a fourth taper angle relative to the longitudinal axis of the gas cylinder and the throughbore, which is slightly greater than the first taper angle. The upper portion cooperates with a first similarly-shaped portion of the gas cylinder to prevent wobbling of the cylinder relative to the base. The upper segment of the ring portion engages a second similarly-shaped portion of the gas cylinder to preclude longitudinal movement of the cylinder relative to the base. In the preferred embodiment, the first taper angle is approximately 1.degree., the second taper angle is approximately 35.degree., the third taper angle is approximately 31.degree. and the fourth taper angle is approximately 3.degree.. The medial segment of the ring portion is further engageable with a third similarly-shaped portion of the gas cylinder.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.